What P0143 means
Sensor 3 is a third oxygen sensor on bank 1, behind a second converter or converter brick.
How the engine computer detects it
It only exists on some vehicles – documented for Jaguar Land Rover's 3.0 V6 supercharged (2013–2016, where sensor 2 is 'mid-cat' and sensor 3 'post-cat') and Ford systems that monitor part of the converter volume. P0143 means the signal of sensor 3 stays below its lower limit – typically a short to ground, or on some systems an open circuit. Jaguar Land Rover assigns it to the post-cat sensor; Ford applies the same pull-up resistance check as for sensor 2 (open above 1 MΩ, short below 10 Ω). Code-specific thresholds for sensor 3 are not published. When it fails, the control module stops the downstream trim and cannot evaluate the converter; there is no limp mode.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Check engine light on (usually after two drive cycles)
- Catalyst monitor readiness not set
- Usually no noticeable change in driving
Common causes
- Signal wire shorted to ground or melted against the exhaust Most likely
- Sensor faulty (cracked element, thermal shock from water) Most likely
- Signal circuit open (counts as low on Ford) Possible
- Exhaust leak ahead of the sensor (lean reading) Possible
How to diagnose P0143
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: oxygen sensor bank1 sensor3, oxygen sensor wiring, catalytic converter.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- 1
- Fuel and air metering
- 43
- Specific fault
Questions drivers ask
Can I drive with code P0143?
Usually yes for a short time, if the car drives normally, the temperature gauge reads normal and the check engine light is steady. If the light flashes, the engine loses power or overheats, or other warning lights come on, pull over and have it checked.
Will my car pass an emissions inspection with P0143?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
Will P0143 clear by itself?
The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.
Can I fix P0143 myself?
Often yes, with an OBD-II scanner and basic tools. Difficulty: easy. Start with the cheapest checks before replacing expensive parts.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.